Causes
Itch (pruritus) has many causes. Allergies and inflammatory skin disease all produce itch as a symptom. Pathophysiologically, the sensation of the itch is poorly understood. Nevertheless, there are many known inducers of itch. Histamine is wildly known as an inducer of the itch sensation. Other substances known to induce itch are substance P, cytokines, and proteases.
Temperature also has an effect. It is conventional opinion that applied cold temperature inhibits itch by inhibiting C-fiber activity. However, studies have also described paradoxical phenomena associated with temperature and itch, where applied short-term moderate cold temperature stimulus enhanced the itch. Such a phenomenon might be explained by "paradoxical heat", which is when one has the perception of heat when, in fact, the skin is innocuously cooled. Thus, the exact effect of temperature on itch remains unclear, with different levels of heat and cold proven to both enhance and inhibit itch.
Alcohol is known to have close interactions with histamine release. Alcohol both stimulates the release of histamine from mast cells and inhibits its degradations by inhibiting diamine oxidase. Though histamine is used by the body to mediate alcohol-induced gastric and intestinal damage as well as alcohol flushing, it is possible that elevated levels of histamine might have a correlation with referred itch (or even itch in general).
Read more about this topic: Referred Itch